Isoform-Specific Localization Diversifies Human MSI2 Function.

Area of Science:

• Molecular Biology
• Cell Biology
• Cancer Research

Background:

• Musashi-2 (MSI2) is an RNA-binding protein with diverse regulatory roles in gene expression, including translation and mRNA stability.
• The varied functions of MSI2, sometimes contradictory within the same cellular environment, have remained mechanistically unexplained.

Purpose of the Study:

• To elucidate the molecular basis for the diverse regulatory activities of Musashi-2 (MSI2).
• To investigate the role of alternative splicing in determining MSI2's subcellular localization and function.

Main Methods:

• Tethered reporter assays were employed to assess MSI2 isoform-specific translational activity.
• Truncation and mutation analyses were performed to identify functional domains.
• Isoform localization was determined, and protein interaction networks were mapped using mass spectrometry.

Main Results:

• Alternative splicing generates MSI2 isoforms with distinct subcellular localizations: MSI2-328 in the cytoplasm and MSI2-324 in the nucleus.
• The MSI2-328 isoform enhances translation, while the MSI2-324 isoform does not.
• A specific 18-amino acid sequence, arising from alternative splicing, dictates nuclear localization and loss of translational activation.
• MSI2 isoforms interact with different protein partners, including translation factors (MSI2-328) and chromatin modifiers (MSI2-324).
• The MSI2-324 isoform is more abundant in several cancer types.

Conclusions:

• Alternative splicing is a key determinant of MSI2's regulatory function by controlling its subcellular localization and protein interactions.
• These findings provide a mechanistic framework for understanding the context-dependent roles of MSI2 in gene regulation, stem cell biology, and cancer.